Modern, high speed, automated concrete block plants and concrete paver plants make use of concrete block molds that are open at the top and bottom. These molds are mounted in machines that cyclically station a pallet below the mold to close the bottom of the mold, deliver dry cast concrete into the mold through the open top of the mold and densify and compact the concrete by a combination of vibration and pressure, and then strip the uncured blocks from the mold by relative vertical movement between the mold and the pallet. For efficient high-volume production, concrete block molds are typically configured to produce multiple blocks simultaneously. A concrete block mold generally comprises two side walls and two end walls (outside division plates) that define the periphery of a mold cavity. Within this mold cavity, inside division plates may be used to sub-divide the mold cavity into a plurality of block-forming cavities. The division plates, whether inside or outside, are generally rectangular-shaped plates attached to the side walls of the mold. Further, the side walls of the block cavity and the division plates may be covered with replaceable mold face linings to protect the mold components from abrasive wear.
As disclosed in U.S. Pat. No. 7,208,112, the complete disclosure of which is incorporated by reference herein, some blocks are formed with patterned, decorative, three-dimensional front faces while retaining the high-speed, mass production of the blocks. As disclosed in U.S. Pat. No. 7,208,112, the blocks can be formed front-face up in the mold, allowing the front face of the block to be contacted by a stripper shoe that imparts a desired three-dimensional pattern to the front face. When a block is formed front-face up in the mold, most of the top and bottom surfaces of the blocks (from the perspective of the block as laid in a wall) are formed by division plates. The side surfaces of the block preferably converge to allow the blocks to be laid up in a curved or radiused wall, making the front of the block wider than the rear of the block. For such a block formed front-face up to be discharged through the bottom of the mold, the side surfaces of a block must be formed by moveable side walls that, in a first position during molding, form the wider front portion and narrower bottom portion of the block, and in a second position during discharge of the block from the mold, moves sufficiently out of the way for the wider front portion of the block to pass through the bottom of the mold.
Some blocks are made to include a flange or lip that extends below the bottom of the block. The lip is designed to abut against the rear face of a like block in the course below that particular block to provide a predetermined set-back from the course below and provide course-to-course shear strength. To manufacture the block in a high speed concrete block mold process, the inside division plates and typically one of the outside division plates have an undercut or instep portion along the bottom edge. The undercut portion, in combination with the pallet that is introduced under the mold to temporarily close the open mold bottom during processing, defines a lip-forming subcavity. The lip-forming subcavity has a shape that results in the formation of the lip on the block. If the lips are not completely formed, there can be resulting problems. Such resulting problems may include a jagged edge at the interface between the lip and the bottom face of the block. This results in a wider inside lip radius. A wider inside lip radius may cause an upper block laid up on a lower block to ride forward, thus creating a forward pitch to the wall system. This can lead to an unstable wall.
Thus, there is a need for a mold and process that provide for an improved block, in which the inside lip radius is controlled.